The present invention relates to subterranean treatments and, more particularly, in certain embodiments, to swellable spacer fluids for sealing an annular space in a well bore, such as the annular space between a tubular and a subterranean formation, between two concentric tubulars, or for forming a seal in a subterranean formation.
Spacer fluids are commonly placed between one or more fluids contained in or to be pumped into a well bore. Among other things, a spacer fluid may be used to prevent intermixing between two incompatible fluids and could potentially provide increased compatibility should the incompatible fluids unintentionally intermix. For example, in primary cementing, a spacer fluid may be used to separate a cement composition and a drilling fluid, which may be incompatible. In addition, a spacer fluid may condition the surface of the pipe to promote a better cement bond. Moreover, a spacer fluid may be placed into the well bore between a cement composition and a drilling fluid to provide improved displacement of the drilling fluid from the well bore, thereby potentially improving bonding of the cement composition to the subterranean formation. Once a spacer fluid is in its final location within the well bore, a spacer fluid may act to provide continued separation of a cement composition from a drilling fluid. A spacer fluid may also be used to minimize or remove a filter cake from the formation.
The composition of a spacer fluid is generally tailored to the specific application. In some instances, a spacer fluid may comprise an aqueous fluid, a viscosifying agent, a weighting agent, and a surfactant. Among other things, the weighting agent may be included in the spacer fluid to provide increased density for well control and also increase the buoyancy effect of the spacer fluid on a viscosified drilling fluid and filter cake adhered to the walls of the well bore. Viscosifying agents may be included in spacer fluids to provide desirable rheological properties for suspending particle stability and fluid loss control. The surfactants may be included in the spacer fluids to enhance chemical compatibility of the spacer fluid with the other fluids in the well bore and to provide water-wet formation surfaces to improve cement bonding or to promote or minimize the entrainment of gases into the fluid.